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Global warming
For Wikipedia: List of scientists # The earth's climate system has warmed significantly over the past century. AR4 Topic 1, 1.1 # Most of the recent global warming was very likely caused by human activity increasing the atmospheric concentrations of greenhouse gases. AR4 Topic 2, 2.2, # Anthropogenic global warming is continuing today and will likely accelerate in the coming decades. AR4 Topic 3, 3.1, AR4 Topic 3, 3.2 # Left unchecked, global warming will have catastrophic consequences for human civilization. AR4 Topic 3, 3.3 (3.3.1, 3.3.2, 3.3.3, 3.3.4, 3.3.5), AR4 Topic 6, 6.2 ---- # The earth's climate system has warmed significantly over the past century. #: "Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice and rising global average sea level." AR4 Topic 1, 1.1 # Most of the recent global warming was very likely caused by human activity increasing the atmospheric concentrations of greenhouse gases. #: "Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations." AR4 Topic 2, 2.2 #: "It is likely that there has been significant anthropogenic warming over the past 50 years averaged over each continent (except Antarctica)." AR4 Topic 2, 2.2 # Anthropogenic global warming is continuing today and will likely accelerate in the coming decades. #: "There is high agreement and much evidence that with current climate change mitigation policies and related sustainable development practices, global GHG emissions will continue to grow over the next few decades." AR4 Topic 3, 3.1 #: "For the next two decades a warming of about 0.2°C per decade is projected for a range of SRES emissions scenarios. Even if the concentrations of all GHGs and aerosols had been kept constant at year 2000 levels, a further warming of about 0.1°C per decade would be expected." AR4 Topic 3, 3.2 # Left unchecked, global warming will have catastrophic consequences for human civilization. #: "More specific information is now available across a wide range of systems and sectors concerning the nature of future impacts." AR4 Topic 3, 3.3 #: – 3.3.1 Impacts on systems and sectors #: – 3.3.2 Impacts on regions #: – 3.3.3 Especially affected systems, sectors and regions #: – 3.3.4 Ocean acidification #: – 3.3.5 Extreme events #: "Some systems, sectors and regions are likely to be especially affected by climate change. ... Recent events have demonstrated the vulnerability of some sectors and regions, including in developed countries, to heat waves, tropical cyclones, floods and drought." AR4 Topic 6 (Robust findings), 6.2 Topic 1 brings together information from Working Groups I and II on observed changes in climate and the effects of past climate change on natural systems and human society.   Topic 2 addresses causes of change, considering both natural and anthropogenic drivers of climate change. It analyses the chain including greenhouse gas emissions and concentrations, to radiative forcing and resultant climate change, and evaluates whether observed changes in climate and in physical and biological systems can be attributed to natural or anthropogenic causes. In providing that information it draws on information contained in all three Working Group contributions to the AR4.   Topic 3 presents information from the three Working Group reports on projected future climate change and its impacts. It provides updated information on emissions scenarios and projected future changes in climate in the 21st century and beyond, and describes the projected impacts of future climate change on systems, sectors and regions. Special attention is given to issues of human well-being and development.   Topic 4 describes adaptation and mitigation options and responses as assessed in the reports of Working Groups II and III, and the inter-relationship of climate change and response measures with sustainable development. The focus of this topic is on response measures that can be implemented by 2030. Technologies, policies, measures and instruments as well as barriers to implementation are addressed along with synergies and trade-offs.   Topic 5 covers the long-term perspective and analyses scientific, technical and socio-economic aspects relevant to adaptation and mitigation, consistent with the objectives and provisions of the United Nations Framework Convention on Climate Change (UNFCCC). It places decision-making about climate change in a risk management perspective, paying attention to broader environmental and integration issues. The topic describes emissions trajectories for stabilisation of greenhouse gas concentrations at various levels and associated temperature increases, along with information about the costs of mitigation, required technology development and deployment, and avoided climate impacts. It also explores in detail five main reasons for concern regarding climate change, which it finds have become stronger due to new knowledge since the TAR.   Topic 6 highlights robust findings and key uncertainties.  From Wikipedia: Global Warming Global warming is the observed century-scale rise in the average temperature of Earth's climate system.2 Since 1971, 90% of the increased energy has been stored in the oceans, mostly in the 0 to 700m region.3 Despite the oceans' dominant role in energy storage, the term "global warming" is also used to refer to increases in average temperature of the air and sea at Earth's surface.4 Since the early 20th century, the global air and sea surface temperature has increased about 0.8 °C (1.4 °F), with about two-thirds of the increase occurring since 1980.5 Each of the last three decades has been successively warmer at the Earth's surface than any preceding decade since 1850.6 Scientific understanding of the cause of global warming has been increasing. In its fourth assessment (AR4 2007) of the relevant scientific literature, the Intergovernmental Panel on Climate Change (IPCC) reported that scientists were more than 90% certain that most of global warming was being caused by increasing concentrations of greenhouse gases produced by human activities.789 In 2010 that finding was recognized by the national science academies of all major industrialized nations.10a Affirming these findings in 2013, the IPCC stated that the largest driver of global warming is carbon dioxide (CO2) emissions from fossil fuel combustion, cement production, and land use changes such as deforestation.12 Its 2013 report states: : Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climate extremes. This evidence for human influence has grown since AR4. It is extremely likely (95-100%) that human influence has been the dominant cause of the observed warming since the mid-20th century. - IPCC AR5 WG1 Summary for Policymakers13 Climate model projections were summarized in the 2013 Fifth Assessment Report (AR5) by the Intergovernmental Panel on Climate Change (IPCC). They indicated that during the 21st century the global surface temperature is likely to rise a further 0.3 to 1.7 °C (0.5 to 3.1 °F) for their lowest emissions scenario using stringent mitigation and 2.6 to 4.8 °C (4.7 to 8.6 °F) for their highest.14 The ranges of these estimates arise from the use of models with differing sensitivity to greenhouse gas concentrations.1516 Future climate change and associated impacts will vary from region to region around the globe.1718 The effects of an increase in global temperature include a rise in sea levels and a change in the amount and pattern of precipitation, as well as a probable expansion of subtropical deserts.19 Warming is expected to be strongest in the Arctic, with the continuing retreat of glaciers, permafrost and sea ice. Other likely effects of the warming include more frequent extreme weather events including heat waves, droughts and heavy rainfall; ocean acidification; and species extinctions due to shifting temperature regimes. Effects significant to humans include the threat to food security from decreasing crop yields and the loss of habitat from inundation.2021 Proposed policy responses to global warming include mitigation by emissions reduction, adaptation to its effects, building systems resilient to its effects, and possible future climate engineering. Most countries are parties to the United Nations Framework Convention on Climate Change (UNFCCC),22 whose ultimate objective is to prevent dangerous anthropogenic (i.e., human-induced) climate change.23 Parties to the UNFCCC have adopted a range of policies designed to reduce greenhouse gas emissions24252627 and to assist in adaptation to global warming.24272829 Parties to the UNFCCC have agreed that deep cuts in emissions are required,30 and that future global warming should be limited to below 2.0 °C (3.6 °F) relative to the pre-industrial level.30b Reports published in 2011 by the United Nations Environment Programme31 and the International Energy Agency32 suggest that efforts as of the early 21st century to reduce emissions may be inadequate to meet the UNFCCC's 2 °C target. Emissions of greenhouse gases grew 2.2% per year between 2000 and 2010, compared with 1.3% per year from 1970 to 2000.33 China currently leads the world in global CO2 emissions.